Coil on Plug Ignition Systems
There are many types of ignition systems used throughout the years and things are continuing to evolve. The coil on plug COP ignition systems stage eliminates the distributor and secondary wires and replaces them with an ECM, ignition module, and a coil mounted directly on the plug of each cylinder of the engine. This system is very efficient.
In order to properly diagnose a misfire on one or all of the cylinders, it is important to understand the system you are working with. Let's have a look at the components that make up a typical coil on pack ignition system.
Coil on plug (COP) coils: The coil shown in the illustration is a typical coil that integrates the ignition module into the coil itself. The primary and the secondary circuits are both located in an automotive coil, and a COP type coil is no exception. It's where the two meet. If there is no power coming to the coil from the ECM neither circuit gets power and the coil will not fire. As you can see the trigger is the control circuit and the ground circuit speaks for itself.
In other common type of COP system the trigger circuit is a feedback circuit performing a different function. This feedback circuit is used to inform the PCM of the cylinders firing. In this type of system the ignition module is located inside the PCM. A PCM and an ECM perform the same function with different names and acronyms, they control engine all functions. PCM stands for power train control module and ECM stands for engine control module. The difference usually indicates whether it is an import (ECM) or domestic (PCM).
Related wiring: Make sure the connectors, wires, and harness are in proper operating condition with a good visual inspection. Sometimes the connectors have locks that when damaged during removal will not snap into place correctly. Check these connectors by pulling lightly on the plug to make sure it correctly seated into it's companion socket. Check any suspected wiring for resistance with an ohmmeter and compare with manufacturers specifications.
Ignition Control Module: The ignition control module takes place of the distributor in a distributorless ignition system. It receives it's timing instructions from the ECM based on input from the crankshaft and camshaft sensors and sends the appropriate signal to the appropriate cylinder. The IM may be stand alone, located in the ECM, or integral to each ignition coil like the COP coil used in the illustration.
Engine Control Module: The ECM may or may not contain the ignition control module. It takes input from the crankshaft and camshaft sensors and calculates ignition timing by comparing it to preset instructions. It then sends this signal to each coil associated with the cylinder in the correct firing order. An open between the ECM and a cylinder's coil or a faulty ECM driver will result in no power and a misfire on that cylinder.
Crankshaft and Camshaft sensors: These sensors send the crankshaft and camshafts position signals to the ECM for interpretation. These signals will be used for ignition and fuel injection timing.
